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From: Hans Petter Selasky <hselasky@FreeBSD.org>
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Subject: PERFORCE change 168461 for review
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http://perforce.freebsd.org/chv.cgi?CH=168461

Change 168461 by hselasky@hselasky_laptop001 on 2009/09/12 10:45:51

	
	USB CORE:
	
	 - add extra safety locking when clobbering
	 xfer->flags_int.started in start and stop
	 functions, because xfer->flags_int is also
	 updated by the USB controller, under the
	 controller lock.
	
	 - fix a comment.

Affected files ...

.. //depot/projects/usb/src/sys/dev/usb/usb_transfer.c#168 edit

Differences ...

==== //depot/projects/usb/src/sys/dev/usb/usb_transfer.c#168 (text+ko) ====

@@ -1622,7 +1622,10 @@
 	/* mark the USB transfer started */
 
 	if (!xfer->flags_int.started) {
+		/* lock the BUS lock to avoid races updating flags_int */
+		USB_BUS_LOCK(xfer->xroot->bus);
 		xfer->flags_int.started = 1;
+		USB_BUS_UNLOCK(xfer->xroot->bus);
 	}
 	/* check if the USB transfer callback is already transferring */
 
@@ -1657,14 +1660,21 @@
 	/* check if the USB transfer was ever opened */
 
 	if (!xfer->flags_int.open) {
-		/* nothing to do except clearing the "started" flag */
-		xfer->flags_int.started = 0;
+		if (xfer->flags_int.started) {
+			/* nothing to do except clearing the "started" flag */
+			/* lock the BUS lock to avoid races updating flags_int */
+			USB_BUS_LOCK(xfer->xroot->bus);
+			xfer->flags_int.started = 0;
+			USB_BUS_UNLOCK(xfer->xroot->bus);
+		}
 		return;
 	}
 	/* try to stop the current USB transfer */
 
 	USB_BUS_LOCK(xfer->xroot->bus);
-	xfer->error = USB_ERR_CANCELLED;/* override any previous error */
+	/* override any previous error */
+	xfer->error = USB_ERR_CANCELLED;
+
 	/*
 	 * Clear "open" and "started" when both private and USB lock
 	 * is locked so that we don't get a race updating "flags_int"